It uses the a prompt for the user to input a password or request. The page is dynamically built based on the the user response. It uses an external *.js file (If referenced directly, it will download) that contains arrays to build the page. You should not rely on this for secure pages, but give a good example for low in content management.
It's a bit clunky, but shows how to use to create dynamic page changes. I have used an external *.js file for site navigation.